Very helpful !! I made my first baffle last night with the help of this Post. My Betta, Flotsom is enjoying the softer current exploring the parts of the tank he couldn't swim before the baffle. Thanks again!!

I posted a question about this as well. I have a closed filter already with a sponge on the intake, and I put one inside the filter. I raised the water level which I consider to be too high. It doesn't look like a baffle would work in this case. This is someone's youtube video of my filter:

I have an Aqueon quietflow 30 on my 10 gallon and I"m missing it's hood and blue piece (the part after the filter holder..) .. I haven't done the waterbottle trick but I put on a Fluval pre filter sponge on the intake and on the spill out since it's a nice long flat piece I put a Aquaclear sponge cut in half so it's still the same height .. and stuck it on the outflow and my hood holds it in place. Needless to say my betta loves it and also so does my dwarf water lettuce. It stays perfectly in place now!

I wanted comment on how to make this safer for the fish and human fingers. The edges could be sharp. So I suggest slicing air tubing on one side pushing it onto the edges of the baffle so it's covering the the sharp edges.

I had a pantyhose baffle on mine but I noticed after a while there was a cloudy film gathering around it, I guess because after a while all the crud from the water gathers on it, it was gross and I threw it away. Just used my only water bottle to make another baffle and it's awesome. Didn't need tape or string or anything to hold it on either, it just stays there lol There is still a bit of a current but this seems much more sanitary and is far less of an eyesore than the pantyhose was.

As jadaBlue mentioned the edges were a little ragged and jagged from the scissor cut and I was worried about my little guy's fins so I used a lighter to melt the edges and it's much safer now. But be careful if you do it this way, of course there is fire involved so be careful anyways, but if you hold the plastic too close to the flame it curls, just hold it to the edge of the flame to melt the very edge of the plastic. And be sure to melt all the edges that will be in the water, so every edge but the one on the top sticking out of the water lol